Tales of Trenzalore", will be published by BBC Digital 27 Feb, 2014. Four authors and four stories - "Let it Snow", by Justin Richards, George Mann's "An Apple a Day", Paul Finch has written one called "Strangers in the Outland", and finally there's one by Mark Morris called "The Dreaming". Amazon is selling it for the Kindle for £2.49.
Here's the description:
"As it had been foretold, the armies of the Universe gathered at
Trenzalore. Only one thing stood between the planet and destruction -
the Doctor. For nine hundred years, he defended the planet, and the
tiny town of Christmas, against the forces that would destroy it."
never knew how long he could keep the peace. He never knew what
creatures would emerge from the snowy night to threaten him next. He
knew only that at the end he would die on Trenzalore."
"Some of what happened during those terrible years is well documented. But most of it remains shrouded in mystery and darkness.
"This is a glimpse of just some
of the terrors the people faced, the monstrous threats the Doctor
defeated. These are the tales of the monsters who found themselves
afraid - and of the one man who was not."